Western diplomats fear if the Iranians don’t RSVP very soon, it will be logistically difficult to put together a meeting for next week.

American officials have interpreted the Iranian delay in scheduling talks to date as a potentially inauspicious sign of continued dysfunction or indecisiveness in Tehran, diplomatic sources tell the Back Channel.

American negotiators “are ready, if Iran says yes, to work through with them a step by step deal,” a Washington non-proliferation expert told the Back Channel Tuesday. “They want to be able to make a deal. And a major concern is whether Iran is capable of making a deal, whether the Supreme Leader is capable of even deciding that he wants to make a deal. That is where their concern is.”

Some Iran analysts have speculated Iran may be stalling amid suggestions the six nation negotiating group has only modestly updated the offer they plan to present to Iran at the next meeting. “Weeks of deliberations among the United States and its fellow negotiators have produced an offer to Iran very similar to the package Iran rejected last summer, casting doubt on chances for breaking the long stalemate over Iran’s nuclear program,” Barbara Slavin reported at Al-Monitor last month.

“We can over-think this and imagine the Iranians are reacting negatively to the [P5+1] package,” Daryl Kimball, executive director of the Arms Control Association, told the Back Channel. “But the Iranians don’t know what the new package is.”

Iran has frequently played such tactical games with negotiators, raising last minute objections to proposed venues, for instance, leaving some convinced last summer they were not yet serious about a deal. Iranian officials in turn express misgivings about whether the West is prepared to make and honor the terms of a deal.

“One of the problems is the P5+1 are limited by the simple fact that they are dealing with six countries. …so you get the least common denominator,” Kimball added.

That cumbersome dynamic is one key reason the US has reportedly quietly pressed Iran through emissaries to agree to direct talks. But as yet, there is no sign that Iran has agreed–which might be another factor in Iran's delay in RSVP'ing to the P5+1 talks.

Iran is scheduled to host a senior team from the International Atomic Energy Agency (IAEA) on January 16th.

Update: Still no agreement from Iran on a date for talks, a western diplomat said Friday.